Evaporator for refrigeration plant delimiting two respectively high-pressure and low-pressure evaporation chambers and separated by a filter screen

ABSTRACT

An evaporator for a refrigeration plant including a high-pressure chamber, a low-pressure chamber, a filter screen interposed between the high-pressure chamber and the low-pressure chamber, and a communication conduit linking the high-pressure chamber to the low-pressure chamber. The filter screen passes the working fluid in the gaseous phase from the high-pressure chamber towards the low-pressure chamber, and blocks the passage of the working fluid in the liquid phase from the high-pressure chamber towards the low-pressure chamber and vice versa. The communication conduit essentially allows the working fluid in the liquid phase to pass from the high-pressure chamber to the low-pressure chamber, and opposes a free passage of the working fluid in the gaseous phase from the high-pressure chamber to the low-pressure chamber and vice versa.

TECHNICAL FIELD OF THE INVENTION

The present invention concerns firstly an evaporator for refrigerationplant where the refrigeration plant includes a circuit in which aworking fluid circulates, the evaporator comprising a main chambercontaining a working fluid where a gaseous phase and a liquid phase ofsaid working fluid coexist, said main chamber comprising a supply inletintended to be connected to the circuit to supply the main chamber withworking fluid in the liquid state and an extraction outlet intended toextract from the main chamber working fluid in the gaseous state towardsthe circuit, the evaporator comprising a heat exchange device capable ofheating the working fluid contained in the main chamber.

The invention also concerns a refrigeration plant comprising such anevaporator.

The invention finds an application in particular in the refrigerationplants intended for the production of artificial snow, in therefrigeration plants intended for the production of ice, for example forthe food industry, or even in the refrigeration plants intended to beintegrated into an air conditioning and cold production system, forexample for cooling data management computer center.

STATE OF THE ART

It is known that a refrigeration plant comprises a circuit in which aworking fluid circulates and the following elements staggered along thecircuit and through which the working fluid circulates successively: anevaporator for heat exchange with a cold source, the working fluidundergoing a loss of calories due to the evaporation, a compressionmachine and a condenser with possibly an exchanger for heat exchangewith a hot source.

Such a refrigeration plant corresponds, for example, to the teachings ofthe document WO2019/020940A1 in the name of the Applicant.

It turns out that the phenomenon of evaporation which occurs in theevaporator is likely to be accompanied by a certain boiling or bubblingof the working fluid, which may cause the transfer of droplets of theworking fluid in the direction of the compression machine.

This risk increases especially since the pressure and the density of thegas within the evaporator decrease, taking into account the increase inthe ratio between the density of the liquid compared to that of the gas.

One of the difficulties is to succeed in overcoming these problems whenthe working fluid is for example essentially water-based, possibly withcertain additives. For an evaporation pressure of 6 mbar, the volumeratio between the gas and the liquid may be greater than 200000 and theevaporation in the evaporator may be very explosive, with a very highrisk of seeing droplets being carried towards the compression machine.This may cause malfunctions or maintenance problems of the compressionmachine and this is not satisfactory.

It has already been designed to place an anti-droplet screen at theoutlet of the evaporator, but the simulations show that the pressuredrops are too high and affect the general operation of the refrigerationplant.

Even if the above issues are presented in connection with theessentially water-based working fluid, they are likely to arise forother natures of fluid, for example methyl ethylene glycol.

OBJECT OF THE INVENTION

The purpose of the present invention is to provide an evaporator and arefrigeration plant which respond to the problems presented above inconnection with the state of the art.

In particular, the aim of the invention is to provide a solution whichmeets at least one of the following objectives:

-   -   be economical and efficient,    -   limit the internal pressure drops,    -   avoid any risk of damage to the compression machine due to the        evaporator,    -   be operational and effective in the case where the working fluid        is essentially water-based.

This object may be achieved by providing an evaporator for refrigerationplant where the refrigeration plant includes a circuit in which aworking fluid circulates, the evaporator comprising a main chambercontaining a working fluid where a gaseous phase and a liquid phase ofsaid working fluid coexist, said main chamber comprising a supply inletintended to be connected to the circuit to supply the main chamber withworking fluid in the liquid state and an extraction outlet intended toextract from the main chamber working fluid in the gaseous state towardsthe circuit, the evaporator comprising a heat exchange device capable ofheating the working fluid contained in the main chamber, noteworthy inthat the evaporator comprises:

-   -   a high-pressure chamber delimited within the main chamber, at        the level of which the supply inlet is arranged so that the        high-pressure chamber is supplied with working fluid in the        liquid state by the circuit, the high-pressure chamber        containing working fluid in the gaseous phase at a first        pressure value and working fluid in the liquid phase, the        high-pressure chamber delimiting at least one tray containing        the working fluid in the liquid phase present in the        high-pressure chamber, the at least one tray of the        high-pressure chamber providing a surface for evaporation of the        working fluid in the liquid phase contained in the high-pressure        chamber at a first evaporation pressure value,    -   a low-pressure chamber delimited within the main chamber,        containing working fluid in the gaseous phase at a second        pressure value strictly lower than the first pressure value and        working fluid in the liquid phase, the extraction outlet being        arranged at the level of the low-pressure chamber so that        working fluid in the gaseous phase contained in the low-pressure        chamber is extracted towards the circuit, the low-pressure        chamber delimiting at least one tray containing the working        fluid in the liquid phase present in the low-pressure chamber,        the at least one tray of the low-pressure chamber providing a        surface for evaporation of the working fluid in the liquid phase        contained in the low-pressure chamber at a second evaporation        pressure value strictly different from the first evaporation        pressure value,    -   a filter screen interposed between the high-pressure chamber and        the low-pressure chamber, the filter screen allowing the working        fluid in the gaseous phase to pass from the high-pressure        chamber to the low-pressure chamber, and blocking the passage of        the working fluid in the liquid phase from the high-pressure        chamber to the low-pressure chamber and vice versa,    -   a communication conduit linking the high-pressure chamber to the        low-pressure chamber, said communication conduit essentially        allowing the working fluid in the liquid phase to pass from the        high-pressure chamber to the low-pressure chamber, and opposing        a free passage of the working fluid in the gaseous phase from        the high-pressure chamber to the low-pressure chamber and vice        versa.

Certain preferred but non-limiting aspects of this evaporator are thefollowing, taken alone or in combination.

The communication conduit is an overflow-type spill system arranged atthe level of said at least one tray of the high-pressure chamber.

The spill system is configured to act as a siphon between the workingfluid in the liquid phase of at least one tray of the high-pressurechamber and the working fluid in the liquid phase of at least one trayof the low-pressure chamber.

The ratio between the surface for evaporation of the working fluid inthe liquid phase contained in the low-pressure chamber and the surfacefor evaporation of the working fluid in the liquid phase contained inthe high-pressure chamber is greater than 2 and preferably greater thanor equal to 5.

The communication of working fluid in the gaseous phase from thelow-pressure chamber to the circuit is free, devoid of filtration.

The ratio between the mass flow rate of working fluid evaporated in thehigh-pressure chamber and the mass flow rate of working fluid evaporatedin the low-pressure chamber is comprised between 5 and 10.

The ratio between the mass flow rate of working fluid in the gaseousphase circulating through the filter screen and the mass flow rate ofworking fluid in the gaseous phase circulating in the communicationconduit is greater than 100.

The high-pressure chamber comprises at least two trays superimposed andsuccessively supplied with working fluid in the liquid phase by gravityflow through a pouring device fitted to at least one tray of thehigh-pressure chamber.

The low-pressure chamber comprises at least two trays superimposed andsuccessively supplied with working fluid in the liquid phase by gravityflow through a pouring device fitted to at least one tray of thelow-pressure chamber.

The filter screen is a wall, having through pores adapted to allow theworking fluid in the gaseous phase to pass on either side of this wall,and presenting undulations along the height of the wall.

The invention also relates to a refrigeration plant comprising a circuitin which a working fluid circulates, the refrigeration plant comprisingthe following elements staggered along said circuit and through whichthe working fluid circulates successively: an evaporator as mentionedabove in which the working fluid in the liquid phase undergoes a loss ofcalories due to the evaporation occurring in the high-pressure chamberand in the low-pressure chamber, a compression machine, a condenser.

Certain preferred but non-limiting aspects of this refrigeration plantare the following, taken alone or in combination.

The working fluid mainly contains water.

The fact remains that the working fluid may be of another nature, suchas methyl ethylene glycol for example.

The mass flow rate of the gaseous phase of the working fluid circulatingin the circuit is comprised between 15 g/s and 15 kg/s.

The low-pressure chamber of the evaporator comprises a discharge outletallowing to extract from the main chamber working fluid in the liquidphase from the at least one tray of the low-pressure chamber.

The high-pressure chamber of the evaporator comprises an intake pipeallowing to supply at least one tray of the high-pressure chamber withworking fluid in the liquid phase previously extracted from thelow-pressure chamber through the discharge outlet.

The refrigeration plant comprises a second circuit in which anoperational fluid separate from the working fluid circulates and a heatexchanger between the operational fluid circulating in the secondcircuit and the working fluid in the liquid phase present in, orresulting from, the main chamber of the evaporator.

Alternatively, it may be an air conditioning system-like refrigerationplant, comprising an evaporator previously described and in which theworking fluid which circulates in the evaporator being maintained at apressure comprised between 5 and 100 mbar performs a function ofdecontamination against predetermined bacteria, in particularLegionella.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, objects, advantages and characteristics of the inventionwill appear better on reading the following detailed description ofpreferred embodiments thereof, given by way of non-limiting example, andmade with reference to the appended drawings on which:

FIG. 1 is a schematic sectional view of an example of a refrigerationplant comprising a first example of an evaporator according to theinvention.

FIG. 2 is a schematic sectional view of an example of a refrigerationplant comprising a second example of an evaporator according to theinvention.

DETAILED DESCRIPTION

In FIGS. 1 and 2 and in the rest of the description, the same referencesrepresent identical or similar elements. In addition, the differentelements are not necessarily represented to scale so as to favor theclarity of the figures if necessary. Furthermore, the differentembodiments and variants are not mutually exclusive and may, on thecontrary, be combined with each other.

The invention relates firstly to an evaporator 10 for a refrigerationplant 100 where the refrigeration plant 100 includes a circuit 50 inwhich a working fluid circulates, the evaporator 10 comprising a mainchamber 11 containing a working fluid where a gaseous phase and a liquidphase of the working fluid coexist.

The main chamber 11 comprises a supply inlet 12 intended to be connectedto the circuit 50 to supply the main chamber 11 with working fluid inthe liquid state and an extraction outlet 13 intended to extract fromthe chamber main 11 working fluid in the gaseous state towards thecircuit 50, in order to supply the compression machine 60.

The evaporator 10 also comprises a heat exchange device 70 capable ofheating the working fluid contained in the main chamber 11.

According to a particular non-limiting application, the refrigerationplant 100 with which the evaporator 10 described in the present documentis associated is a refrigeration plant corresponding to the teachings ofthe document WO2019/020940A1 in the name of the Applicant.

The invention finds an application in particular in the refrigerationplants intended for the production of artificial snow, in therefrigeration plants intended for the production of ice, for example forthe food industry, or even in the refrigeration plants intended to beintegrated into an air conditioning system, for example for cooling datamanagement computer center.

As can be seen in each of the two FIGS. 1 and 2 , the evaporator 10comprises a high-pressure chamber 14 delimited within the main chamber11, at the level of which the supply inlet 12 is arranged so that thehigh-pressure chamber 14 is supplied with working fluid in the liquidstate by the circuit 50.

The high-pressure chamber 14 contains working fluid in the gaseous phase15 at a first pressure value and working fluid in the liquid phase 16.In other words, within the high-pressure chamber 14, the working fluidin the gaseous phase 15 and the working fluid in the liquid phase 16coexist. Advantageously, this first pressure value is comprised between6 and 7 mbar, typically 6.5 mbar, which advantageously allows to providea strong boiling of the liquid (which mixes it and helps heat transfer)but the projections remain contained by the filter screen 24 detailedbelow. One of the goals is to be close to the low-pressure chamber 17 soas not to be boiling in the low-pressure chamber 17.

The high-pressure chamber 14 delimits at least one tray 20 containingthe working fluid in the liquid phase 16 present in the high-pressurechamber 14. The at least one tray 20 of the high-pressure chamberprovides a surface 21 for evaporation of the working fluid in the liquidphase 16 contained in the high-pressure chamber 14, this evaporationtaking place at a first evaporation pressure value. The working fluidthus evaporated mixes with the rest of the working fluid in the gaseousphase 15. The evaporation surface 21 corresponds to the interfacebetween the working fluid in the liquid phase 16 and the working fluidin the gaseous phase. 15. Advantageously, this first evaporationpressure value is comprised between 6 and 7 mbar, typically in the rangeof 6.5 mbar.

The evaporator 10 also comprises a low-pressure chamber 17 delimitedwithin the main chamber 11, containing working fluid in the gaseousphase 18 at a second pressure value strictly lower than the firstpressure value and working fluid in the liquid phase 19. In other words,within the low-pressure chamber 17, the working fluid in the gaseousphase 18 and the working fluid in the liquid phase 19 coexist.Typically, this second pressure value is in the range of 6.11 mbar, inorder to avoid boiling and therefore avoid having any projection.

The extraction outlet 13 is arranged at the level of the low-pressurechamber 17 so that the working fluid in the gaseous phase 18 containedin the low-pressure chamber 17 is extracted in the direction of thecircuit 50 until it is supplied the compression machine 60. Thecompression machine 60 allows on the one hand to transfer the materialwith a certain volume flow rate, on the other hand to maintain apressure ratio between the delivery pressure and the suction pressure.The nature of the compression machine 60 is not limiting, comprising oneor several compression stages and possibly a compression rate higher,equal to, or greater than 10.

The low-pressure chamber 17 delimits at least one tray 22 containing theworking fluid in the liquid phase 19 present in the low-pressure chamber17. The at least one tray 22 of the low-pressure chamber 17 provides asurface 23 for evaporation of the working fluid in the liquid phase 19contained in the low-pressure chamber 17, this evaporation taking placeat a second evaporation pressure value strictly different from the firstevaporation pressure value. The working fluid thus evaporated mixes withthe rest of the working fluid in the gaseous phase 18. The evaporationsurface 23 corresponds to the interface between the working fluid in theliquid phase 19 and the working fluid in the gaseous phase 18.Typically, this second evaporation pressure value is in the range of6.11 mbar.

The evaporator 10 also comprises a filter screen 24 interposed betweenthe high-pressure chamber 14 and the low-pressure chamber 17. The filterscreen 24 is configured so as to allow the working fluid in the gaseousphase 15 to pass from the high-pressure chamber 14 to the low-pressurechamber 17 so that it mixes with the working fluid in the gaseous phase18, and to block the passage of the working fluid in the liquid phase 16from the high-pressure chamber 14 to the low-pressure chamber 17. Thefilter screen 24 acts to prevent projections of working fluid in theliquid phase 16 from reaching the compression machine 60 and ensuresthat the liquid thus blocked falls back by gravity into the tray 20 fromwhich it was projected during the evaporation. A person skilled in theart is able, based on his general knowledge, to design a filter screen24 that meets these functions, the structure of the filter screen 24 notbeing limiting in itself.

The evaporator 10 comprises a communication conduit 25 linking thehigh-pressure chamber 14 to the low-pressure chamber 17. Thecommunication conduit 25 is configured so as to essentially allow theworking fluid in the liquid phase 16 to pass from the high-pressurechamber 14 to the low-pressure chamber 17 and to oppose a free passageof the working fluid in the gaseous phase 15 from the high-pressurechamber 14 to the low-pressure chamber 17 and to oppose a free passageof the working fluid in the gaseous phase 18 from the low-pressurechamber 17 to the high-pressure chamber 14.

A person skilled in the art is able, based on his general knowledge, todesign a communication conduit 25 that meets these functions, thestructure of the communication conduit 25 not being limiting in itself.

According to a non-limiting embodiment, the ratio between the mass flowrate of working fluid in the gaseous phase circulating through thefilter screen 24 and the mass flow rate of working fluid in the gaseousphase circulating in the communication conduit 25 is greater than 100,or even preferably greater than 1000, or even more preferably greaterthan 10,000. The mass flow rate of working fluid in the gaseous phasewhich would possibly circulate through the communication conduit 25 isin fact considered as an unsought leak, even harmful. It is thereforesought a mass flow rate of working fluid in the gaseous phase whichwould possibly circulate through the communication conduit 25 as closeto 0 as possible.

According to an advantageous embodiment in terms of simplicity andefficiency, the communication conduit 25 is an overflow-type spillsystem arranged at the level of at least one tray 20 of thehigh-pressure chamber 14, adapted to spill the excess working fluid inthe liquid phase 16 contained in this at least one tray 20 into the atleast one tray 22 arranged in the low-pressure chamber 17.

According to a non-limiting embodiment, and as shown, this spill systemis configured to act like a siphon between the working fluid in theliquid phase 16 of at least one tray 20 of the high-pressure chamber 14and the working fluid in the liquid phase 19 of at least one tray 22 ofthe low-pressure chamber. This can be obtained by arranging a simpletube, an upper end of which opens into this tray 20 and a lower end ofwhich is arranged in the volume of this tray 22. The positioning of theupper end of the tube fixes the height of the working fluid in theliquid phase 16 in the concerned tray 20 and the lower end fixes theheight of the working fluid is embedded in the working fluid in theliquid phase 19 contained in the concerned tray 22.

According to a non-limiting embodiment, the ratio between the surface 23for evaporation of the working fluid in the liquid phase 19 contained inthe low-pressure chamber 17 and the surface 21 for evaporation of theworking fluid in the liquid phase 16 contained in the high-pressurechamber 14 is greater than 2 and preferably greater than or equal to 5.These arrangements guaranteeing a large evaporation surface make itpossible not to be boiling in the low-pressure chamber 17.

As shown schematically in FIGS. 1 and 2 , the working fluidcommunication in the gaseous phase 18 of the low-pressure chamber 17towards the circuit 50 is free and devoid of filtration. This makes itpossible to reduce internal pressure drops as much as possible, therebyimproving operating efficiency. It is possible to afford this type ofarrangement due to the very organization of the evaporator 10 with thefilter screen 24 which blocks the liquid projections which appear in thezones where violent evaporations occur and the fact that the evaporationoccurring in the low-pressure chamber 17 takes place at low-pressure ina manner which in itself avoids the risk of liquid projections.

According to a non-limiting embodiment, the ratio between the mass flowrate of working fluid evaporated in the high-pressure chamber 14 at thelevel of the evaporation surface 21 and the mass flow rate of workingfluid evaporated in the low-pressure chamber 17 at the level of theevaporation surface 23 is comprised between 5 and 10. In general, thechoice and adaptation of this ratio results from a compromise betweenthe dimensions of the chamber, the size of the filter screen 24 andrisks of boiling in the low-pressure chamber 17.

Referring to FIG. 2 and unlike the embodiment of FIG. 1 where thehigh-pressure chamber 14 comprises a single tray 20 arranged in itslower part in the manner of a simple receptacle, the high-pressurechamber 14 comprises at least two trays 20 (for example three in numberas illustrated) superposed and successively supplied in cascade withworking fluid in the liquid phase 16 by gravity flow through a pouringdevice 26 fitted to each tray 20 of the high-pressure chamber 14 exceptthe furthest downstream. The boiling is then only possible on the top (afew centimeters) of the liquid because below, the hydrostatic pressureprevents the boiling. The boiling acts as an agitator in the heattransfer.

In combination with the arrangements of the previous paragraph or inisolation, and still with reference to FIG. 2 and unlike the embodimentof FIG. 1 where the low-pressure chamber 17 comprises a single tray 22arranged in its lower part at the manner of a simple gravity receptaclefor liquid, the low-pressure chamber 17 may comprise at least two trays20 (for example three in number as illustrated) superimposed andsupplied successively in cascade with a working fluid in the liquidphase 19 by gravity flow through a pouring device 27 fitted to each tray22 of the low-pressure chamber 17 except the furthest downstream. Theexchange surface is then increased for the same diameter of the tank(this in relation to the ratio between the surface 23 for evaporation ofthe working fluid in the liquid phase 19 contained in the low-pressurechamber 17 and the surface 21 for evaporation of the working fluid inthe liquid phase 16 contained in the high-pressure chamber 14).

From the foregoing, it can be understood that the high-pressure chamber14 may optionally include a single tray 20 while the low-pressurechamber 17 would include several trays 22 organized as described above.Alternatively, the low-pressure chamber 17 may optionally include asingle tray 22 while the high-pressure chamber 14 would include severaltrays 20 organized as described above. These possible arrangements arenot illustrated.

According to a non-limiting embodiment, the filter screen 24 is a wall,having through pores (not shown in detail) suitable to allow the workingfluid in the gaseous phase 15, 18 to pass on either side of this wall,and having undulations 28 along the height of the wall. The wall can bevertical, horizontal, or oblique. According to one possible embodiment,it is possible to integrate metal or plastic straw to agglomerate thedrops and then baffles to stop them.

The invention also relates to a refrigeration plant 100 comprising acircuit 50 in which the working fluid circulates, the refrigerationplant 100 comprising the following elements staggered along the circuit50 and through which the working fluid circulates successively: anevaporator 10 as previously described in which the working fluid in theliquid phase undergoes a loss of calories due to the evaporationoccurring in the high-pressure chamber 14 and in the low-pressurechamber 17, a compression machine 60, a condenser 80 where the workingfluid undergoes liquefaction, the condensates 90 being sent, via thecircuit 50, to the supply inlet 12.

Advantageously, the working fluid contains at least one aqueous fluid,essentially water, optionally with some additives such as glycol.

According to a non-limiting embodiment, the mass flow rate of thegaseous phase of the working fluid circulating in the circuit 50 iscomprised between 15 g/s and 15 kg/s.

As represented in each of FIGS. 1 and 2 , the low-pressure chamber 17 ofthe evaporator 10 comprises a discharge outlet 29 making it possible toextract from the main chamber 11 working fluid in the liquid phase 19from at least one tray 22 of the low-pressure chamber 14. Thesearrangements make it possible to extract from the evaporator 10 theliquid working fluid previously cooled in the evaporator 10 as a resultof the double evaporation occurring respectively in the high-pressurechamber 14 and in the low-pressure chamber 17, this allowing use of thefluid thus extracted.

After having been used, the liquid working fluid previously extracted atthe discharge outlet 29 is reinjected into the high-pressure chamber 14.To this end, it is advantageous to provide that the high-pressurechamber 14 of the evaporator 10 comprises an intake pipe 30 allowing tosupply at least one tray 20 of the high-pressure chamber 14 with workingfluid in the liquid phase 16 previously extracted from the low-pressurechamber 17 through the discharge outlet 29.

In a first possible use where the working fluid is the fluid intended tobe used by the customer, the liquid working fluid previously extractedat the discharge outlet 29 is directly exploited by the customer, thelatter using the advantage of the fact that it has been previouslycooled in the evaporator 10.

According to a particularly advantageous embodiment where therefrigeration plant 100 is an air conditioning system, the cooling ofthe working fluid (which is in particular essentially aqueous) whichcirculates in the evaporator 10 while being maintained at a pressurelevel comprised between 5 and 100 mbar ensures a decontaminationfunction against predetermined bacteria, in particular Legionella. It isthe very low-pressure (between 5 and 100 mbar) in the evaporator 10which ensures the destruction of the bacteria. Indeed, a pressure levelcontained in this range typically corresponds to a temperature comprisedbetween 25° C. and 45° C., this temperature range being favored for thedevelopment of the Legionella bacteria.

In another possible use, the refrigeration plant 100 comprises a secondcircuit (not represented) in which circulates an operational fluiddistinct from the working fluid and a heat exchanger (not represented)between the operational fluid circulating in the second circuit and theworking fluid in the liquid phase present in, or coming from, the mainchamber 11 of the evaporator 10. Such a heat exchanger can therefore bearranged inside or outside the main chamber 11 of the evaporator 10.

The invention which has just been described has the advantage of beingeconomical and efficient, of limiting the internal pressure drops to theevaporator 10 and to the refrigeration plant 100, of avoiding any riskof damage to the compression machine 60 due to the evaporator 10, and tobe operational and efficient in the event that the working fluid isessentially water-based.

1. An evaporator for a refrigeration plant where the refrigeration plantincludes a circuit in which a working fluid circulates, the evaporatorcomprising a main chamber containing a working fluid where a gaseousphase and a liquid phase of the working fluid coexist, the main chambercomprising a supply inlet intended to be connected to the circuit tosupply the main chamber with working fluid in the liquid state and anextraction outlet intended to extract from the main chamber workingfluid in the gaseous state towards the circuit, the evaporatorcomprising a heat exchange device capable of heating the working fluidcontained in the main chamber, wherein the evaporator comprises: ahigh-pressure chamber delimited within the main chamber, at which thesupply inlet is arranged so that the high-pressure chamber is suppliedwith working fluid in the liquid state through the circuit, thehigh-pressure chamber containing working fluid in the gaseous phase at afirst pressure value and working fluid in the liquid phase, thehigh-pressure chamber delimiting at least one tray containing theworking fluid in the liquid phase present in the high-pressure chamber,the at least one tray of the high-pressure chamber providing a surfacefor evaporation of the working fluid in the liquid phase contained inthe high-pressure chamber to a first evaporation pressure value, alow-pressure chamber delimited within the main chamber, containing aworking fluid in the gaseous phase at a second pressure value strictlylower than the first pressure value and a working fluid in the liquidphase, the extraction outlet being arranged at the level of thelow-pressure chamber so that a working fluid in the gaseous phasecontained in the low-pressure chamber is extracted towards the circuit,the low-pressure chamber delimiting at least one tray containing theworking fluid in the liquid phase present in the low-pressure chamber,the at least one tray of the low-pressure chamber providing a surfacefor evaporation of the working fluid in the liquid phase contained inthe low-pressure chamber at a second evaporation pressure value strictlydifferent from the first evaporation pressure value, a filter screeninterposed between the high-pressure chamber and the low-pressurechamber, the filter screen allowing the working fluid at the gaseousphase to pass from the high-pressure chamber to the low-pressurechamber, and blocking the passage of the working fluid in the liquidphase from the high-pressure chamber towards the low-pressure chamberand vice versa, a communication conduit linking the high-pressurechamber to the low-pressure chamber, the communication conduitessentially allowing the working fluid in the liquid phase to pass fromthe high-pressure chamber towards the low-pressure chamber, and opposinga free passage of the working fluid in the gaseous phase from thehigh-pressure chamber towards the low-pressure chamber and vice versa.2. The evaporator according to claim 1, wherein the communicationconduit is an overflow type spill system arranged at the at least onetray of the high-pressure chamber.
 3. The evaporator according to claim2, wherein the spill system is configured to act in the manner of asiphon between the working fluid in the liquid phase of at least onetray of the high-pressure chamber and the working fluid in the liquidphase of at least one tray of the low-pressure chamber.
 4. Theevaporator according to claim 1, wherein the ratio between the surfacefor evaporation of the working fluid in the liquid phase contained inthe low-pressure chamber and the surface for evaporation of the workingfluid in the liquid phase contained in the high-pressure chamber isgreater than
 2. 5. The evaporator according to claim 1, wherein theworking fluid communication in the gaseous phase from the low-pressurechamber towards the circuit is free, devoid of filtration.
 6. Theevaporator according to claim 1, wherein the ratio between the mass flowrate of working fluid evaporated in the high-pressure chamber and themass flow rate of working fluid evaporated in the low-pressure chamberis comprised between 5 and
 10. 7. The evaporator according to claim 1,wherein the ratio between the mass flow rate of working fluid in thegaseous phase circulating through the filter screen and the mass flowrate of working fluid in the gaseous phase circulating in thecommunication conduit is greater than
 100. 8. The evaporator accordingto claim 1, wherein the high-pressure chamber comprises at least twotrays superimposed and successively supplied with working fluid in theliquid phase by gravity flow through a pouring device fitted to at leastone tray of the high-pressure chamber.
 9. The evaporator according toclaim 1, wherein the low-pressure chamber comprises at least two trayssuperimposed and successively supplied with working fluid in the liquidphase by gravity flow through a pouring device fitted to at least onetray of the low-pressure chamber.
 10. The evaporator according to claim1, wherein the filter screen is a wall, having through pores adapted toallow the working fluid in the gaseous phase to pass on either side ofthis wall, and having undulations along the height of the wall.
 11. Arefrigeration plant comprising a circuit in which a working fluidcirculates, the refrigeration plant comprising the following elementsstaggered along the circuit and through which the working fluidsuccessively circulates: an evaporator according to claim 1 in which theworking fluid in the liquid phase undergoes a loss of calories due tothe evaporation occurring in the high-pressure chamber and in thelow-pressure chamber, a compression machine, a condenser.
 12. Therefrigeration plant according to claim 11, wherein the working fluidcontains essentially water.
 13. The refrigeration plant according toclaim 11, wherein the mass flow rate of the gaseous phase of the workingfluid circulating in the circuit is comprised between 15 g/s and 15kg/s.
 14. The refrigeration plant according to claim 11, wherein thelow-pressure chamber of the evaporator comprises a discharge outletmaking it possible to extract from the main chamber working fluid in theliquid phase from the at least one tray of the low-pressure chamber. 15.The refrigeration plant according to claim 14, wherein the high-pressurechamber of the evaporator comprises an intake pipe making it possible tosupply at least one tray of the high-pressure chamber with working fluidin the liquid phase previously extracted from the low-pressure chamberthrough the discharge outlet.
 16. The refrigeration plant according toclaim 11, wherein the refrigeration plant comprises a second circuit inwhich circulates an operational fluid distinct from the working fluidand a heat exchanger between the operational fluid circulating in thesecond circuit and a working fluid in the liquid phase present in, orcoming from, the main chamber of the evaporator.
 17. The refrigerationplant of the air conditioning system type, comprising an evaporatoraccording to claim 1 and in which the working fluid which circulates inthe evaporator being maintained at a pressure comprised between 5 and100 mbar ensures a decontamination function against predeterminedbacteria.